DOAK Model 16 VZ-4 VTOL Aircraft

The DOAK Model 16, or VZ-4 as it was perhaps better known, was a prototype VTOL aircraft developed by the Doak Aircraft Company for the U.S. Army during the '50s and early '60s.

The aircraft had been proposed to the U.S. Army in 1950 by the company's founder, Edmund R. Doak. The top brass were impressed by the idea of an aircraft which could take off and land vertically, hover, fly backwards, while also offer a higher top speed and longer range than a conventional helicopter.

The DOAK VZ-4 used two ducted fans mounted on the end of its stubby wings for propulsion and lift. The original engine was an 840 horsepower Lycoming YT53 turboprop, but this was later upgraded to a 1,000 horsepower T53-L-1 engine. The fans were positioned vertically for takeoff and landing, and rotated to a horizontal orientation for horizontal flight. The VZ-4 was the first aircraft to use this form of VTOL flight.

The VZ-4 was built around a tubular metal frame with metal wings and a tail section. The nosecone was formed from fiberglass. Various other elements of the aircraft were taken from existing models. The landing gear was from a humble Cessna 182, the duct actuators were lifted from a Lockheed T-33 Shooting Start jet, while the two seats were the same as those used in the North American P-51 Mustang.



The DOAK VZ-4 made its first test flight in early 1958. On February 25th 1958 the aircraft hovered for the first time, and over a year later, in May 1959 the first transition from vertical flight to horizontal flight and back again successfully took place.

Overall the DOAK VZ-4 proved to live up to its expectations, a remarkable feat for a prototype VTOL aircraft, and the very first to explore the rotating ducted-fan layout. However it wasn't without problems. Firstly its VTOL take of and landing performance wasn't great, and during transition from vertical to horizontal flight it had a tendency to nose up.

After further testing during the summer of 1959 the U.S. Army accepted the prototype in September of that year. The aircraft received the designation VZ-4DA and was sent to the NASA Langley Research Center in Hampton, Virginia.

Unfortunately for the VZ-4 project, the Doak Aircraft Company ran into financial problems in 1960, resulting in funding for development for the project being diverted elsewhere. Douglas Aircraft bought the rights and engineering files to continue development, and even hired four engineers from Doak to continue work on the aircraft.

Testing and development of the VZ-4 continued for a further 3 years until the U.S. Army themselves decided that they would put their faith, and money, into conventional helicopters, and they withdrew funding entirely for the project and terminated testing in 1963.

Happily however, the groundbreaking DOAK VZ-4 escaped the crusher, and it is currently held on display at the U.S. Army Transportation Museum at Fort Eustis, Virginia.